Improved photoelectrochemical performance and stability have been achieved via forming heterostructured CdS@g-C3N4 core–shell nanorod arrays.

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The photostability of donor–acceptor (D–A) polymers remains a critical issue despite recent improvements in the power conversion efficiencies (PCEs) of organic photovoltaic (OPV) cells. We report the synthesis of three highly photostable polymers (PDTBDT-BZ, PDTBDT-BZF, and PDTBDT-BZF2) and their suitability for use in high-performance OPV cells. Under 1 sunlight of illumination in air for 10 h, these polymer films demonstrated remarkably high photostability compared to that of PTB7, a representative polymer in the OPV field. While the PDTBDT-BZ, PDTBDT-BZF, and PDTBDT-BZF2 polymer films maintained 97, 90, and 96% photostability, respectively, a PTB7 film exhibited only 38% photostability under the same conditions. We ascribed the high photostability of the polymers to both the intrinsically photostable chemical moieties and the dense packing of alkyl side chains and planar backbone polymer chains, which prevents oxygen diffusion into the PDTBDT-BZ films. This work demonstrates the high photostability of planar PDTBDT-BZ series polymers composed of photostable DTBDT and BZ moieties and suggests a design rule to synthesize highly photostable photovoltaic materials.

It is important to develop new donor (D)− acceptor (A) type low band gap polymers for highly stable polymer solar cells (PSCs). Here, we describe the synthesis and photovoltaic properties of two D−A type low band gap polymers. The polymers consist of dithienobenzodithiophene (DTBDT) moieties with expanded conjugation side groups as donors and 2-ethyl-1-(thieno[3,4-b]thiophen-2-yl)hexan-1-one (TTEH) or 6-octyl-5H-thieno[3′,4′:4,5]thieno[2,3-c]pyrrole-5,7(6H)-dione (DTPD) as acceptors to give pDTBDT-TTEH and pDTBDT-DTPD polymers, respectively. The pDTBDT-TTEH is quite flat, resulting in a highly crystalline film. In contrast, the pDTBDT-DTPD is highly twisted to yield an amorphous film. Photovoltaic devices based on pDTBDT-TTEH and pDTBDT-DTPD exhibited power conversion efficiencies (PCEs) of 6.74% and 4.44%, respectively. The PCE difference results mainly from morphological differences between the two polymer:PC 71 BM blend films; the pDTBDT-TTEH polymer formed a nanoscopically networked domains in the blend state, while the pDTBDT-DTPD polymer film contained aggregated domains with large phase separation between the polymer and PC 71 BM molecules. Importantly, we observed that pDTBDT-TTEH-based devices showed excellent stabilityin air, retaining 95% of the initial PCE after storage for over 1000 h without encapsulation. The high stability of the pDTBDT-TTEH-based device was originated mainly by the crystalline nature of the pDTBDT-TTEH:PC 71 BM film. This work suggests that designing highly conjugated planar backboned polymers is crucial to improve not only the photovoltaic performance but also the stability of PSCs.

We report the synthesis, characterization, and solar cell properties of new donor−acceptor-type low band gap polymers (POBDTPD and PEBDTPD) that incorporate dialkoxybenzodithiophene (BDT) as the donor and N-octyl-2,7-dithia-5-azacyclopenta[a]pentalene-4,6-dione (DTPD) as the acceptor. The newly developed DTPD moiety was carefully designed to lower a band gap via strong interaction between donor−acceptor moieties and keep polymer energy levels deep. Remarkably, the DTPD acceptor moiety effectively widens the light absorption range of the polymers up to ∼900 nm while positioning their HOMO and LUMO levels in the optimal range, i.e., −5.3 and −4.0 eV, respectively, for high power conversion efficiencies (PCEs) as we intended. Solar cell devices were fabricated according to the structure ITO/ PEDOT:PSS/photoactive (polymer:PC 70 BM)/TiO 2 /Al. The POBDTPD devices exhibited a PCE of 4.7% with a V oc of 0.70 V, a J sc of 10.6 mA/cm 2 , and a FF of 0.64. The PEBDTPD devices yielded a higher PCE of 5.3% with a V oc of 0.72 V, a J sc of 13.5 mA/cm 2 , and a FF of 0.54. AFM, TEM, and PL quenching measurements revealed that the high J sc s are a result of the appropriate morphology and efficient charge separation. In comparing the performances of the two polymer devices, the higher J sc for the PEBDTPD device was attributed to its better nanoscale phase separation, smoother surface, and higher carrier mobility in the polymer:PC 70 BM blend films. The higher FF for the POBDTPD device was ascribed to a good balance between the hole and electron mobilities. Overall, we demonstrate that the DTPD unit is a promising electron-accepting moiety to develop high performance low band gap polymers.